Amanda Hoh and Rania Spooner

The search area for missing flight MH370 is no closer to being refined and authorities are still operating on "guesstimates" weeks after crews started scouring the Indian Ocean, Prime Minister Tony Abbott has said.

Mr Abbott, who on Monday visited the Pearce RAAF base in Perth, conceded search personnel were operating on limited information with wreckage parts yet to be confirmed in what he described as ''an extraordinarily difficult'' mission.

MH370: Perth takes centre stage

''Until we locate some actual wreckage from the aircraft and then do the regression analysis that might tell us where the aircraft went into the ocean, we'll be operating on guesstimates,'' he said.

Although Australia is currently bearing the costs of its part in the search operation, which includes a new co-ordination centre in Perth, Mr Abbott said "tallying" would be conducted between the involved countries at some point.

Prime Minister Tony Abbott has paid tribute to the 550 personnel involved in the search for the missing plane from the Pearce RAAF base. Photo: Alex Ellinghausen

About 35 distraught family members of those missing with the plane have arrived in Kuala Lumpur to remonstrate with Malaysian authorities, rather than travel Perth to be closer to the search.

On Monday the Australian search of an area about 1850km off the Perth coast involved 10 aircraft and 10 ships.

But the ADV Ocean Shield, which is carrying the mission's only black box pinger locator, has been delayed departing from a Perth naval base.

The Ocean Shield was due to leave HMAS Stirling about 9pm to undertake equipment trials near Rottnest Island before heading for the search zone, but has been delayed by an hour and half.

The Ocean Shield could still be another four days away from the search zone and the man responsible for the black box search, Captain Mark Matthews, has described the mission as ''untenable''.

The international air and sea search effort for missing flight MH370 will continue to ''ramp up'' over the coming days with ongoing involvement from Malaysia, the United States, New Zealand, China, Japan and Korea.

On Monday, more than 100 people in the air and about 1000 sailors in the area are searching for anything that may be linked to the missing flight. Australian crews have been flying three and four consecutive 12-hour missions.

''In a humanitarian cause the nations of this region can come together to work for the betterment of humanity, to work to try to resolve this extraordinary mystery," Mr Abbott said.

''They can work to try to bring peace and closure to the families of the 239 people on board that ill-fated aircraft.''

Mr Abbott said although ''the best brains in the world'' were being applied to find MH370 the difficulty of locating the wreckage could not be underestimated.

''This is an extraordinarily difficult exercise, we are searching a vast area of ocean and we are working on a quite limited information,'' he said.

''If this mystery is solvable, we will solve it, but I don't want to underestimate how difficult it is.''

Despite the lack of solid, physical evidence, Mr Abbott backed the decision by Malaysian Prime Minister Najib Razak last week to declare the aircraft and its passengers lost.

''The accumulation of the evidence is that the aircraft has been lost and it has been lost somewhere in the south of the Indian Ocean,'' he said.

''I think that Prime Minister Najib Razak was perfectly entitled to come to that conclusion and I think once that conclusion had been arrived at, it was his duty to make that conclusion public.''

Former Defence chief Angus Houston, who has been appointed to head a 20-person incident co-ordination team based out of Perth, was at the RAAF base being briefed Monday morning.

He said his team would operate as a liaison point for the families of those on flight MH370, as well as the national and international branches of the search.

''I will obviously be focused very much on co-ordination. I'm not here to run the search, I'm not here to do the detailed operational side of things that's being taken of by the Australian Maritime Safety Authority and the Defence Force,'' he said.

In the air on Sunday an Australian P3 Orion crew reported sighting at least four orange objects, each about two metres in size, floating in an area of about four nautical miles within the search zone.

The sightings have been reported to the search coordination centre and a GPS buoy dropped on the location.

Mr Abbott said he would not put a time limit on the Australian search.

''We owe it to everyone to do whatever we reasonably can and we can keep searching for quite some time to come and we will keep searching for quite some time to come,'' he said.

''The intensity of our search and the magnitude of our operations is increasing, not decreasing.''

Opposition Leader Bill Shorten also paid tribute to those involved in the search after visiting the Pearce RAAF base on Monday afternoon.

“I am certainly convinced that if that plane or debris from the plane can be found or if it is in this area, it will be found by these talented and committed people," he said.

Mr Shorten said “artificial deadlines” for the search should be avoided and that any discussion as to the cost of the operation for Australia “should be dealt with after this mission is completed”.

“At the tip of this exercise of finding the answers, you see people at RAAF base Pearce in Perth.

“I think we need to get behind them rather than necessarily setting deadlines. All we need to do is less theories and leave it more to the practical experts," Mr Shorten said.